1. Field of the Invention
This invention generally relates to systems and methods for implementing storage area networks. More specifically, this invention relates to a method and apparatus that provides fast and efficient routing between subnets in an Infiniband network. Further, this invention relates to a method and apparatus that couples disjoint subnets into a single logical subnet, and that may provide aliasing of IB ports to facilitate the creation of virtual subnets.
2. Description of Related Art
Internetworking of high-performance computers has become the focus of much attention in the data communications industry. Performance improvements in processors and peripherals, along with the move to distributed architectures such as client/server configurations, have spawned increasingly data-intensive and high-speed networking applications, such as medical imaging, multimedia, and scientific visualization. Various protocols have been developed to provide the necessary communications capacity.
A protocol known as Infiniband can carry data over a given link at rates exceeding 2.5 Gbps in each direction. The Infiniband standard provides a point-to-point, switched architecture that allows many devices to concurrently communicate with high-bandwidth and low latency in a protected, remotely managed environment. An end node can communicate over multiple ports, and multiple communications paths may be used between end nodes. Properly exploited, the multiplicity of ports and paths provide both fault tolerance and increased data transfer bandwidth.
An Infiniband (IB) network interconnects end nodes. Each end node may be a processor node, an I/O unit, and/or a router to another network. The IB network is subdivided into subnets that are interconnected by routers. The subnets comprise subnet managers, switches, and the end nodes linked to the switches. (Technically, a single link between two end nodes is also considered a subnet, with one of the end nodes functioning as a subnet manager for that link. However, this degenerate case is neglected herein.) Multiple links may exist between any two of the devices.
Packets are directed through the IB network using either path-based (“directed route”) or destination-based addressing. Directed-route addressing is reserved for subnet management communications, and may be used before the forwarding tables have been initialized in the switches and routers. Directed-route packets include two lists of port numbers that define a path through the subnet. Each list specifies, in order, the output port of each switch along the path. One list specifies the forward route, and the other specifies the reverse route. The packets also include a direction bit to indicate which list is being followed, and a pointer to indicate the current position in the list. The reverse route list is built by the switches as the packet traverses them.
In destination-based addressing, the packets include either a unicast identifier of a single destination end node, or a multicast identifier of a set of destination end nodes. A multicast set can be defined by an end node and used thereafter. The subnet manager configures the switches with routing information to specify all of the ports where a multicast packet needs to travel. Switches receiving a multicast packet will replicate the packet and send it out to each of the designated ports except the arrival port.
In an Infiniband network, communication occurs at two levels: local (intra-subnet) and global (inter-subnet). Each end node has a global identifier (GID) and a shorter, local identifier (LID). For local communications within a given subnet, LIDs are sufficient to identify the source and destination nodes. For communications that pass between subnets, however, GIDs are required. End nodes in a subnet are interconnected by switches that receive and forward packets based on the LIDs. In turn, subnets are interconnected by routers that receive packets and forward the packets based on GIDs.
Unlike switches, the routers must process the packets to replace the source and destination LIDs in the packet with those appropriate for the current subnet. Such processing must occur at astonishing speeds to prevent the router from becoming a bottleneck in the network. Yet, such performance commonly requires unduly expensive hardware. Consumers would benefit from an architecture that provides such performance at an affordable price. Consumers would further benefit if such a router architecture provided additional features such as connecting disjoint subnets into a single virtual subnet, thereby eliminating the need for closely-related end nodes in separate subnets to communicate at the global level. Consumers would yet further benefit from simplification and centralization of network management that the virtual subnet creation would make possible. Such benefits of virtual subnets would be facilitated if routers provided LID aliasing for end nodes in separate subnets.